This invention relates generally to the field of micro-electrical-mechanical systems (MEMS), and in particular, to improved MEMS devices and methods of making same for use with fiber-optic communications systems.
The Internet and data communications are causing an explosion in the global demand for bandwidth. Fiber optic telecommunications systems are currently deploying a relatively new technology called dense wavelength division multiplexing (DWDM) to expand the capacity of new and existing optical fiber systems to help satisfy this demand. In DWDM, multiple wavelengths of light simultaneously transport information through a single optical fiber. Each wavelength operates as an individual channel carrying a stream of data. The carrying capacity of a fiber is multiplied by the number of DWDM channels used. Today DWDM systems employing up to 80 channels are available from multiple manufacturers, with more promised in the future.
In all telecommunication networks, there is the need to connect individual channels (or circuits) to individual destination points, such as an end customer or to another network. Systems that perform these functions are called cross-connects. Additionally, there is the need to add or drop particular channels at an intermediate point. Systems that perform these functions are called add-drop multiplexers (ADMs). All of these networking functions are currently performed by electronicsxe2x80x94typically an electronic SONET/SDH system. However SONET/SDH systems are designed to process only a single optical channel. Multi-wavelength systems would require multiple SONET/SDH systems operating in parallel to process the many optical channels. This makes it difficult and expensive to scale DWDM networks using SONET/SDH technology.
The alternative is an all-optical network. Optical networks designed to operate at the wavelength level are commonly called xe2x80x9cwavelength routing networksxe2x80x9d or xe2x80x9coptical transport networksxe2x80x9d (OTN). In a wavelength routing network, the individual wavelengths in a DWDM fiber must be manageable. New types of photonic network elements operating at the wavelength level are required to perform the cross-connect, ADM and other network switching functions. Two of the primary functions are optical add-drop multiplexers (OADM) and wavelength-selective cross-connects (WSXC).
In order to perform wavelength routing functions optically today, the light stream must first be de-multiplexed or filtered into its many individual wavelengths, each on an individual optical fiber. Then each individual wavelength must be directed toward its target fiber using a large array of optical switches commonly called an optical cross-connect (OXC). Finally, all of the wavelengths must be re-multiplexed before continuing on through the destination fiber. This compound process is complex, very expensive, decreases system reliability and complicates system management. The OXC in particular is a technical challenge. A typical 40-80 channel DWDM system will require thousands of switches to fully cross-connect all the wavelengths. Opto-mechanical switches, which offer acceptable optical specifications are too big, expensive and unreliable for widespread deployment. Improvements are needed to help reliably switch and direct the various wavelengths along their desired paths.
Micro-electrical-mechanical systems (MEMS) theoretically provide small systems capable of providing switching functions. However, MEMS also have difficulties to overcome. For example, flexures that rotate the MEMS mirror typically are located outside the mirror perimeter. As a result, multiple mirrors in an array are not packed as tightly together as desired. Further, the MEMS mirrors tend to stick to the underlying surface when in the actuated positions, hindering their operation. The present invention is, therefore, directed to improved MEMS devices for use with a wide range of OTN equipment, including switches (OXC) and routers.
The present invention provides improved MEMS devices for use with all optical networks, and methods of using and making same. For example, the present invention may be used with the exemplary wavelength routers described in U.S. Pat. No. 6,501,877, filed Nov. 16, 1999, and issued Dec. 31, 2002, the complete disclosure of which is incorporated herein by reference.
In one embodiment of the present invention, an apparatus for steering light includes a base layer and a folded flexure assembly coupled thereto. A beam layer overlies and is coupled to the folded flexure assembly, with the folded flexure assembly completely underlying the beam layer. The beam layer is adapted to rotate relative to the base layer. In one aspect, the beam layer has a substantially planar upper surface adapted to reflect electromagnetic energy.
In one aspect, the base layer further includes first and second electrically conductive portions that are physically and electrically isolated from each other. The first electrically conductive portion is coupled to a voltage source, with the beam layer adapted to rotate when a voltage is applied to the first electrically conductive portion. In one aspect, the beam layer comprises an electrically conductive material.
In one embodiment, the folded flexure further includes a first arm coupled to the base layer and a second arm coupled to the beam layer. The first and second arms are coupled together, with the coupled portion of the arms disposed between the beam and base layers.
In one aspect, the first and second arms are substantially parallel to each other when the beam layer is in a non-rotated state. In another aspect, the arms are in a non-parallel alignment when the beam layer is in a rotated state. The first and second arms may have, in one embodiment, a thickness between about 0.5 microns and about 2.0 microns. Further, light steering apparatus in other embodiments include a second pair or additional pairs of arms to facilitate beam layer rotation while providing sufficient support thereof.
In one aspect, first and second raised portions are coupled to the base layer. Raised portions may, but need not, extend substantially a full width of the base layer. Raised portions operate as stops, with the beam layer adapted to contact the first and second raised portions when rotated in a first or second direction, respectively. In one aspect, the first and second raised portions are positioned on or in the base layer to define the maximum angles of rotation in the first and second directions. In a particular embodiment, the beam layer has a non-rotated state and a rotated state defining an angle therebetween, with the angle ranging between about one (1) degree and about thirty (30) degrees.
In one embodiment, the folded flexure assembly is adapted to provide a restoring force to the beam layer when the beam layer is in a rotated state. In one aspect, the restoring force is of sufficient strength to prevent the beam layer from sticking to the first and second raised portions, or to the base layer.
In another embodiment, an apparatus for steering light according to the present invention includes a flexure assembly that is adapted to permit an electrode-induced rotation of a beam layer when a voltage is applied, with the flexure assembly further providing a counter-rotation force generally opposite the electrode-induced rotation. In a particular embodiment, the counter-rotation force prevents the beam layer from remaining in a rotated state when the voltage is removed.
In one aspect, the beam layer rotates about an axis of rotation. The flexure assembly further includes a first arm coupled to the base layer on a first side of the axis of rotation, and coupled to the beam layer on a second side of the axis of rotation. A second flexure assembly arm is coupled to the base layer on the second side of the axis of rotation, and is coupled to the beam layer on the first side of the axis of rotation. In this manner, the two arms each provide a rotational force that is generally opposite or counter to the beam layer rotation.
In one aspect, the conductive layer is coupled to a voltage source, with the beam layer being adapted to rotate when a voltage is applied to the conductive layer. In another aspect, the beam layer comprises an electrically conductive material, such as polysilicon, gold or other metals, and the like.
In still another aspect, the beam layer has a non-rotated state and a rotated state defining an angle therebetween, with the angle ranging between about one (1) degree and about thirty (30) degrees. In another aspect, the angle is between about minus one (xe2x88x921) degree to about minus thirty (xe2x88x9230) degrees. Other angular relationships also are within the scope of the present invention.
In another aspect, the flexure assembly is entirely underlying the beam layer. Such a configuration facilitates tight or close packing of multiple apparatus of the present invention. In alternate embodiments, the flexure assembly comprises a conductive or semi-conductive material, such as polysilicon, metals or the like, or a non-conductive material, such as silicon dioxide and other dielectrics.
In another embodiment, a structure for steering light according to the present invention includes a base, an electrode overlying the base, a flexure assembly and a reflective layer coupled to the flexure assembly. The flexure assembly is adapted to permit the reflective layer to move into a rotated state when a voltage is applied to the electrode, with the rotated state having a portion of the reflective layer contacting the base. The flexure assembly further prevents the reflective layer from remaining in the rotated state when the voltage is removed.
Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description, the appended claims and the accompanying drawings.